From e3c6451d5f03074dac3c8221a2ab38f45d8d3451 Mon Sep 17 00:00:00 2001
From: Kevin Robert Stravers <kevin@stravers.net>
Date: Sat, 21 Sep 2024 02:56:04 -0400
Subject: [PATCH] nix repl: Print which variables are just loaded

When we run `nix repl nixpkgs` we get "Added 6 variables". This is not
useful as it doesn't tell us which variables the flake has exported to
our global repl scope.

This patch prints the name of each variable that was just loaded. We
currently cap printing to 10 variables in order to avoid excessive
prints.

https://github.com/NixOS/nix/issues/11404
---
 src/libcmd/repl.cc       | 19 +++++++++++++++++++
 tests/functional/repl.sh | 28 ++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 940b16dfd..da01a3105 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -791,6 +791,25 @@ void NixRepl::addAttrsToScope(Value & attrs)
     staticEnv->sort();
     staticEnv->deduplicate();
     notice("Added %1% variables.", attrs.attrs()->size());
+
+    const int max_print = 10;
+    int counter = 0;
+    std::string loaded;
+    for (auto & i : attrs.attrs()->lexicographicOrder(state->symbols)) {
+        if (counter >= max_print)
+            break;
+
+        if (counter > 0)
+            loaded += ", ";
+
+        loaded += state->symbols[i->name];
+        counter += 1;
+    }
+
+    notice("- %1%", loaded);
+
+    if (attrs.attrs()->size() > max_print)
+        notice("... and %1% more", attrs.attrs()->size() - max_print);
 }
 
 
diff --git a/tests/functional/repl.sh b/tests/functional/repl.sh
index 706e0f5db..0fbf07765 100755
--- a/tests/functional/repl.sh
+++ b/tests/functional/repl.sh
@@ -153,6 +153,32 @@ foo + baz
 ' "3" \
     ./flake ./flake\#bar --experimental-features 'flakes'
 
+testReplResponse $'
+:a { a = 1; b = 2; longerName = 3; "with spaces" = 4; }
+' 'Added 4 variables.
+- a, b, longerName, with spaces
+'
+
+cat <<EOF > attribute-set.nix
+{
+    a = 1;
+    b = 2;
+    longerName = 3;
+    "with spaces" = 4;
+}
+EOF
+testReplResponse '
+:l ./attribute-set.nix
+' 'Added 4 variables.
+- a, b, longerName, with spaces
+'
+
+testReplResponseNoRegex $'
+:a builtins.foldl\' (x: y: x // y) {} (map (x: { ${builtins.toString x} = x; }) (builtins.genList (x: x) 13))
+' 'Added 13 variables.
+- 0, 1, 10, 11, 12, 2, 3, 4, 5, 6
+... and 3 more'
+
 # Test the `:reload` mechansim with flakes:
 # - Eval `./flake#changingThing`
 # - Modify the flake
@@ -302,6 +328,8 @@ runRepl () {
       -e "s@$testDirNoUnderscores@/path/to/tests/functional@g" \
       -e "s@$nixVersion@<nix version>@g" \
       -e "s@Added [0-9]* variables@Added <number omitted> variables@g" \
+      -e '/^- /d' \
+      -e '/\.\.\. and [0-9]* more/d' \
     | grep -vF $'warning: you don\'t have Internet access; disabling some network-dependent features' \
     ;
 }